1. Field of the Invention
The present invention relates to the field of semiconductor manufacturing, and more specifically to the field of chemical-mechanical polishing methods and apparatus for the conditioning and rinsing of polishing pads used in semiconductor manufacturing.
2. Background Information
In semiconductor manufacturing chemical-mechanical polishing is used to ensure planar topography in the fabrication of integrated circuits and other semiconductor devices. One particular type of chemical-mechanical polisher is an orbital polisher.
FIG. 1 illustrates a cross-sectional view of one preferred embodiment of an orbital polisher. During chemical-mechanical polishing with orbital polisher 100, a semiconductor wafer (wafer) 110 is placed onto polishing pad (pad) 130 which has been coated with an active slurry. Wafer 110 is held in place and pressed downward by carrier 120 with force F.sub.1. Pad 130 is attached to the top of table 140. The downward force and the rotational movement of the pad together with the slurry facilitate the abrasive polishing of the upper surface of the wafer.
In the orbital polisher, illustrated in FIG. 1, an orbital polishing motion is used. As shown in FIG. 1, pad 130 is slightly larger than wafer 110, for example, the pad may be approximately 10 inches in diameter and the wafer may be approximately 8 inches in diameter. FIG. 2a illustrates a top view of pad 130 with wafer 110 which shows the relative size of the wafer to the pad of the orbital polisher. To facilitate the orbital motion polishing process, pad 130 is rotated about orbital axis 131 which is offset from the pad center (P) 132. Additionally, wafer 110 is rotated about its center (W), wafer center axis 111, which is also offset from pad center 132. The orbital motion of pad 130 with respect to wafer 110 is illustrated in FIG. 2b. While pad 130 and wafer 110 are being rotated, slurry is distributed to the wafer/pad interface through a plurality of equally spaced holes 133 formed throughout pad 130. This polishing process is continued until the desired planarity is reached.
During polishing the polishing pad has a tendency to "glaze over" due to the build-up on the pad surface of slurry and other deposits, that result from polishing the wafer. As a result of pad glazing, the pad will not absorb a sufficient amount of slurry and consequently the polishing rate of the chemical-mechanical polisher falls off with time, thus decreasing throughput. To prevent glazing, the polishing pad 130 is mechanically scored or "conditioned".
Conditioning the pad removes the slurry/deposit build-up and roughens the surface of pad 130, by "scoring" the surface of the pad. Scoring the pad roughens the surface of the pad, thus increasing the ability of the pad to absorb slurry and thereby increasing the polishing rate of the system. After or during conditioning, the pad is usually rinsed with water to remove the particles and etc. which were loosened during the conditioning of the pad.
Because the orbital polisher, illustrated in FIG. 1, uses orbital motion (i.e. off-center rotation of the pad) and because pad 130 is only slightly larger than wafer 110, it is not desirable to condition the wafer while simultaneously polishing the wafer. Thus, it is preferable to remove the wafer from the pad during conditioning. Also due to the orbital motion of the orbital polisher 100, a radial conditioner is not likely to be used.
Radial conditioners, as illustrated in FIG. 3, condition a radius of the pad. In other words, the radial conditioner conditions from the edge to the center of the pad and the pad itself is moved concentrically until the radial conditioner conditions the entire pad. An example of a method and apparatus for radial conditioning is described in Breivogal et al., U.S. Pat. No. 5,216,843, issued Jun. 8, 1993, and assigned to the assignee herein. Because of the off-center rotation of pad 130, radial conditioning would be non uniform, i.e. some areas of the pad would be scored more or less than other areas, and certain areas of the pad would not be scored at all. The motion of the pad about the radial conditioner 310 would look much like the motion of the pad about the wafer as illustrated in FIG. 2b, thus the pad would be conditioned in an orbital fashion rather than a concentric fashion.
Concentric conditioning is desirable since it helps with the distribution of the slurry at the pad/wafer interface and also because it allows for more uniform polishing of the wafer. Because the wafer is rotated about its center, i.e. wafer center (W), the wafer motion is concentric. Thus, since the wafer motion is concentric the preferred manner to correct for non-uniform polishing of that wafer is to use a conditioner with a concentric conditioning pattern.
A non-radial type of conditioner is illustrated in FIG. 4. Conditioner 400 works in a similar manner to a windshield-wiper. Conditioner 400 starts in a "park" position to the side of pad 130, it is then rotated back and forth about axis 410, such that arm 420 is moved back and forth over pad 130 scoring the pad surface 430. Arm 420 of conditioner 400 is approximately the same length as the diameter of pad 130 so that the entire pad may be conditioned. However, because the inside velocity (v.sub.i), i.e. the velocity of arm 420 at the point closest to the axis 410, is smaller than the outside velocity (v.sub.o), i.e. the velocity of arm 420 at the point furthest from the axis 410, the scoring of the pad 430 is non-uniform. Also, because conditioner 400 moves in a "windshield-wiper" type motion, conditioner 400 does not provide the desired concentric conditioning of the pad as described above.
Additionally, with respect to conditioner 400, if the pad is being conditioned using a high pressure spray there is a risk that the spray may be splashed all over the inside of the polisher. Because arm 420 is the same length as the diameter of the pad, the spray will not only strike the pad but will also overspray the edges of the pad and splash all over the chemical-mechanical polisher in the areas where the pad is shorter than arm 420. Consequently, after the pad is conditioned and another wafer is placed on the pad for polishing, the spray that has splashed all over the chemical-mechanical polisher could drop onto the wafer or mix with the slurry decreasing the abrasiveness of the slurry and consequently decreasing the polishing rate.
Thus, what is needed is a method and apparatus for conditioning a pad in a chemical-mechanical polisher, such that the pad is conditioned in a concentric and uniform manner, and where a high pressure spray is used the pad may be conditioned without the risk of splashing and overspraying.